Condensing zinc vapor



Patented May 5, 1953 Erwin C. Handwerk, Lehighton,

George T.

Mahler and Llewellyn J Held, Palmerton, Pa., assignors to The New Jersey Zinc Company, New York, N. 'Y., a corporation of New Jersey No Drawing. Application September 2, 1949, 'Serial No. 113,902

4 Claims.

This invention relates to the production of metallic zinc vapor and, more particularly, to the prevention of oxidation of metallic'zinc vapor by oxidizing constituents present in the diluent gases generally accczt'ipanying the vapor.

In metallurgical operations wherein metallic zinc vapor is produced as a primary product, the zinc vapor is generally accompanied by a diluent gas. For example, in zinc smelting operations, the metallic zinc is obtained in the form of vapor diluted with smelting gases. Moreover, in metallic zinc recovery operations wherein impure metallic zinc such as dross is heated to separately recover the zinc in the form of its vapor, oxidation of the zinc is guarded against by the deliberate production in situ, or by the addition, of an inert or reducing gaseous atmosphere. Such diluent gases, regardless of their source, generally comprise carbon monoxide accompaniedby some quantities of carbon dioxide. Water vapor and small amounts of atmospheric oxygen are also found at times in such gases. These oxidizing constituents, comprising particularly carbon dioxide, Water vaporand oxygen, have a pronounced oxidizing effect upon metallic zinc vapor which is undesirable in all operations except those wherein the zinc vapor is deliberately burned to produce zinc oxide. The detrimental effect or" oxidation of the metallic zinc vapor by oxidizing constituents present in a diluent gas is particularly disadvantageous where the metallic zinc vapor isto be condensed to'molten metal, the oxidized zinc vapor resulting in the production of chemical. blue powder and in the building up of rock oxide accretions.

We have now discovered that oxidation of metallic zinc vapor by oxidizing constituents present in a diluent gas containing the zinc vapor may .beprevented or at least reduced to a permissible minimum. This result is effected in accordance with our invention by introducing into the hot gaseous product. containing. the;,metallic zinc vapor anarnount of a crackable hydrocarbon such as to produce by its cracking in situ therein a floating cloud of incandescent nascent carbon,

particles. When the amount of crackable hydrocarbon introduced into the. zinc vapor-containing gases is sufiicient to substantially completely neutralize the oxidizingcapacity of the oxidizing constituentspresent in the gases by converting them to'carbon monoxide or hydrogen, or both, oxidation of the zinc vapor is reduced to a negligible level and any zinc oxide that may have been since theCOz thus formed is promptly'transformed to CO by the incandescent nascent carbon.

Metallurgical operations in which the oxidationof metallic zinc vapor may be reduced in accordance with our invention are any of those wherein a hot gaseous product is produced containing the zinc vapor in admixture with a diluent gas'including an oxidizing constituent. For example, the invention may be practiced with particular advantage in the blast furnace or electric furnace smelting of zinciferous ores. In such smelting operations, an appreciable amount of carbon dioxide is formed in the smelting gases. In the blast furnace operation, a relatively large quantity of carbon dioxide is formed by the introduction of a substantial quantity of air into the smelting zone. In the electric furnace operation, some carbon dioxide is produced by complete combustion of the carbonaceous reducing material, generally by the reaction between carbon monoxide and unreduced metal oxide. Moreover, in operations wherein the diluent gas accompanying the zinc vapor comprises carbon monoxide, asin the case of electric furnace smelting as well as in the case of a zinc distilling operation wherein carbon monoxide is used as the protective atmosphere, the carbon monoxide dissociates to an appreciable extent to carbon dioxide and carbon as the zinc'vapor-containing gases are cooled through a temperature range beginning at that of about the boiling point of zinc. This cooling step may take place within the smelting ordistilling furnace or may take place exteriorly thereof in the course of condensing the metallic zinc vapor. Regardless of where the carbon dioxide production occurs, the benefits of the practice of our invention can be realized by introducing the crackable hydrocarbon into the zinc vapor-containing gases while the latter are at a temperature of at least approximately the boiling point oizin'c. 'It will thus be apparent that the prac tice of our invention is applicable to the treatment of any metallic zinc vapor-containing gaseous atmosphere in which an oxidizing constituent such as carbon dioxide, water vapor or oxygen may be introduced in the course of the production of, metallic zinc vapor or in which the oxidizing constituent may be formed, as by the dissociation of carbon monoxide into carbon dioxide, in the subsequent cooling or the zinc vapor-containing gases.

The crackable hydrocarbons which are useful in practicing our invention are any hydrocarbons, whether of naphthenic, asphaltic or paraffinic nature, natural or synthetic, which crack with the resulting production of nascent carbon at temperatures within the range of about 8001300 C. and, more specifically, at a temperature approximating that of the boiling point of metallic zinc. Accordingly, the expression crackable hydrocarbon is used in this sense herein andinthe claims. The carbon so produced in situ in the hot zinc vapor-bearing gases is very finely divided and, in fact, floats therethrough in a form resembling a cloud of nascent particles of carbon black or highly dispersed soot. These minute particles of carbon are quickly heated to incandescence, and in their glowing nascent state they are particularly effective as a reducing or neutralizing agent for carbon dioxide, water vapor and oxygen.

Regardless of the physical form in which the crackable hydrocarbon is introduced into the hot zinc vapor-containing gases, we have found it to be essential that the hydrocarbon be introduced directly into these gases in such manner that it is not excessively consumed by contact with other oxidizable material. For example, where the crackable hydrocarbon is introduced into the gaseous atmosphere of an electric zinc smelting furnace, the crackable hydrocarbon should be so introduced that it is not consumed by the unreduced charge within the furnace in which latter case the crackable hydrocarbon would be consumed by the charge without reaching the zinc Vapor-containing gaseous atmosphere.

The physical form of the crackable hydrocarbon, or of the material containing the crackable hydrocarbon, introduced into zinc vaporcontaining gases in accordance with our invention may be that of a solid, a liquid, or a gas. As an example of the solid or near-solid form, the crackable hydrocarbon may comprise one or more of the relatively volatile components of bituminous coal or of coal tar introduced as such into the zinc vapor-bearing gases. Liquid crackable hydrocarbons such, for example, as fuel oil, gas oil, kerosene, or the like, may be used with particular advantage. The crackable hydrocarbon may also be in the form of a permanent gas, such as acetylene, natural gas, and the like. Where the crackable hydrocarbon is charged in ostensibly solid form, as in the case of bituminous coal, it may be introduced advantageously either in admixture with, or independently of, other portions of the zinciferous charge to the metallurgical operation, care being taken that the hydrocarbon is so charged that it may be volatilized directly into the zinc vapor-containing atmosphere where it is available for cracking in situ to produce nascent carbon. When the crackable hydrocarbon is charged in the form of a liquid, it may be dripped into the zinc vapor-containing atmosphere. Gaseous hydrocarbons may be similarly introduced directly into the zinc vapor-containing gases. For most effective results, we have found it advantageous to introduce the crackable hydrocarbon into the zinc vapor-containing atmosphere in such amounts at spaced intervals, or at such a rate in the case of substantially continuous introduction, as to maintain a sufficient mass of incandescent floating carbon particles to neutralize the oxidizing influence of the carbon dioxide, oxygen and water vapor normally present in said atmosphere.

The amount of crackable hydrocarbon used in the practice of our invention is not critical but is advantageously correlated to the amount of oxidizing constituents (carbon dioxide, water vapor and oxygen) present in the zinc vapor atmosphere, the amount of oxidizing constituents being ascertained either by analysis or by competent estimation. The amount of crackable hydrocarbon used in practicing the invention is advantageously so chosen that the amount of residual carbon resulting from the cracking of the hydrocarbon at the prevailing temperature III of the zinc vapor-bearing atmosphere is at least theoretically sufficient to convert the oxidizing constituents therein to non-oxidizing gases (carbon monoxide and hydrogen). The use of such an amount of a crackable hydrocarbon will produce within the zinc vapor-bearing atmosphere a floating cloud of incandescent carbon particles. A lesser amount of crackable hydrocarbon is also effective although it leads to less complete protection of the zinc in the zinc vapor-containing gaseous atmosphere. The use of an excessively great amount of crackable hydrocarbons is not only wasteful but tends to hinder effective condensation due to soot in the condenser. The ultimate test for the optimum amount of crackable hydrocarbon to be used in each instance can best be determined by observation of the amount of oxidized zinc vapor which is produced, the oxidized zinc vapor appearing in the form of chemical blue powder and rock oxide accretions. It will be found in practice that progressively increasing amounts of the crackable hydrocarbon will progressively reduce the amount of zinc vapor oxidized to a minimum value and that once the minimum value has been obtained still greater amounts of the crackable hydrocarbon will have no appreciable effect. The attainment of this minimum oxidation of the zinc vapor is generally indicated by the presence in the effluent gases from the zinc vapor-treating stage of an appreciable quantity of unconsumed carbon particles.

The practice of the method of our invention may be illustrated by its incorporation in an electric furnace zinc smelting operation in which the evidence of zinc vapor oxidation was clearly apparent. The smelting process was one carried out in a two-electrode, single phase, electric furnace operating at 300 kilowatts power input for the smelting 0f zinciferous ore. The zinc vapor-bearing smelting gases were withdrawn from the furnace through a side wall opening adjacent the top of the furnace, and these gases were delivered directly to a zinc condenser. The temperature of the zinc vapor-bearing smelting gases passing through the furnace side Wall opening ranged between 850 to 950 C. in the case of rich ores containing 60% Zn and as high as 1000 to 1200 C. in the case of a lean ore containing 20% Zn. Oxidation of zinc vapor in the vicinity of this furnace opening was manifested by troublesome accretions of rock oxide which built up rapidly to such an extent as to largely plug the furnace opening. In order to demonstrate the presence of an oxidizing constituent in the smelting gases passing through the furnace opening, a one-foot section of three-inch diameter graphite electrode was suspended in the line connecting the furnace to the condenser at a position only a few inches away from the condenser side of the furnace opening. After continuing the furnace operation for about 24 hours, the suspended graphite sample was removed and was found to be so corroded in the neighborhood of the discharging furnace gases that its diameter was reduced to about two-thirds of its original dimension.

The method of the present invention was then incorporated in the above-described electric furnace smelting operation by substituting 2.0 parts by weight of bituminous coal for 1.5 parts of the former 12 parts by weight of anthracite coal admixed with parts of zinc ore charged to the furnace. Another similar section of graphite electrode was suspended in the same position as that referred to hereinbefore, and the furnace was operated for a period of about three days before the graphite sample was removed. At the end of this period, the graphit showed no sign of corrosion and no trouble was occasioned by rock oxide accretions. The presence of the volatile components of the bituminous coal in the furnace atmosphere appears to be clearly responsible for the lowering of the content of oxidizing constituents present in the smelting furnace gases. The furnace operation was such that the ore-coal charge was introduced through openings in the furnace roof at intervals of about 6 min-'- utes and was deposited on the surface of the slag bath where it floated until smelted. Under these charging conditions, the volatile matter present in the bituminous coal component of the charge was liberated before the charge had attained a reducing temperature so that the evolved volatile hydrocarbons freely entered the furnace atmosphere where they were cracked to produce a cloud of nascent incandescent carbon.

It will be seen, accordingly, that the practice of our invention leads to a noteworthy reduction in the content of oxidizing constituents present in hot zinc vapor-bearing gases. It is not known to us at present whether the presence of the carbon particles produced by cracking of the hydrocarbon prevents the formation of the oxidizing constituent in the furnace gases or whether it 0 functions to reduce or otherwise neutralize the oxidizing constituents as they are formed. Re;- gardless of the function of the nascent carbon produced in accordance with our invention, the introduction of a crackable hydrocarbon into hot zinc vapor-bearing gases has been found to prevent oxidation of the zinc vapor by oxidizing constituents which would otherwise be present in the gases to such an extent as to appreciably oxidize the zinc vapor.

We claim:

1. In the production of metallic zinc vapor wherein a. hot gaseous product is produced containing the zinc vapor in admixture with a diluent gas including an oxidizing constituent at a temperature within the range of about 800 to 1300 C., the improvement which comprises preventing oxidation of the zinc vapor by said oxidizing constituent within said temperature range by introducing into the hot gaseous product an amount of a crackable hydrocarbon sufficient to produce by its cracking in situ therein a floating cloud of incandescent nascent carbon particles but insulficient to lower the temperature of said hot gaseous product below 800 C., and condensing the resulting zinc vapor to molten massive zinc metal.

2. In the production of metallic zinc vapor wherein a hot gaseous product is produced containing the zinc vapor in admixture with a. diluent gas including an oxidizing constituent at a temperature within the range of about 800- 1300 0., the improvement which comprises preventing oxidation of the zinc vapor by said oxi dizing constituent within said temperature range by introducing into the hot gaseous product an amount of a crackable hydrocarbon in the form or volatile material liberated from bituminous coal sufficient to produce by its cracking in situ therein a floating cloud of incandescent nascent carbon particles but insufiicient to lower the temperature or said hot gaseous product beiow 800 C., and condensing the resulting zinc vapor to molten massive zinc metal.

3. In the production of metallic zinc vapor wherein a hot gaseous product is'produced containing the zinc vapor in admixture with a diluent gas including an oxidizing constituent at a temperature within the range of about 800- i) 0., the improvement which comprises preventing oxidation of the zinc vapor by said oxidizing constituent within said temperature range by introducing into the hot gaseous product an amount of a crackable hydrocarbon in the form of fuel oil sufiicient to produce by its cracking in situ therein a floating cloud of incandescent nascent carbon particles but insufficient to lower the temperature of said hot gaseous product below 800 C., and condensing the resulting zinc vapor to molten massive zinc metal.

4. In the production of metallic zinc vapor wherein a hot gaseous product is produced containing the zinc vapor in admixture with a diluent gas including an oxidizing constituent at a temperature within the range of about 800- 1300" C., the improvement which comprises preventing oxidation of the zinc vapor by said oxidizing constituent within said temperature range by introducing into the hot gaseous product an amount of a crackable hydrocarbon in the form of a normally gaseous hydrocarbon sumcient to produce by its cracking in situ therein a floating cloud of incandescent nascent carbon particles but insufiicient to lower the temperature of said hot gaseous product below 800 0., and condensing the resulting zinc vapor to molten massive zinc metal.

ERWIN C. HANDWERK.

GEORGE T. MAHLER. LLEWELLYN J. HELD.

References Cited in the file of this patent I UNITED STATES PATENTS Number Name Date 766,279 Nagel Aug. 2, 1904 976,557 Dawson Nov. 22, 1910 1,425,661 Kato Aug. 15, 1922 1,927,763 Wejnarth Sept. 19, 1933 1,961,425 Maier June 5, 1934 2,096,779 Bartholomew et al. Oct. 26, 1937 2,263,751 Avery Nov. 25, 1941 2,364,742 Merriam Dec. 12, 1944 OTHER REFERENCES The Condensed Chemical Dictionary 3rd Ed. by Gregory. Published 1942. 

1. IN THE PRODUCTION OF METALLIC ZINC VAPOR WHEREIN A HOT GASEOUS PRODUCT IS PRODUCED CONTAINING THE ZINC VAPOR IN ADMIXTURE WITH A DILUENT GAS INCLUDING AN OXIDIZING CONSTITUENT AT A TEMPERATURE WITHIN THE RANGE OF ABOUT 800* TO 1300* C., THE IMPROVEMENT WHICH COMPRISES PREVENTING OXIDATION OF THE ZINC VAPOR BY SAID OXIDIZING CONSTITUENT WITHIN SAID TEMPERATURE RANGE BY INTRODUCING INTO THE HOT GASEOUS PRODUCT AN AMOUNT OF A CRACKABLE HYDROCARBON SUFFICIENT TO PRODUCE BY ITS CRACKING IN SITU THEREIN A FLOATING CLOUD OF INCANDESCENT NASCENT CARBON PARTICLES BUT INSUFFICIENT TO LOWER THE TEMPERATURE OF SAID HOT GASEOUS PRODUCT BELOW 800* C., AND CONDENSING THE RESULTING ZINC VAPOR TO MOLTEN MASSIVE ZINC METAL. 